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Evolution and
Natural
SelectionJunior Science
Lesson Objectives
Explain what is meant by Variation in a Species.
Analyse the role that environment and genetic factors in variation.
Explain natural selection provides a mechanism for evolution.
Explain the difference between Selective Breeding and Evolution
Understand how Comparative Anatomy can explain evolution.
Only natural selection results in adaptation.
Variation
Variation describes the different traits
which can exist in members of the same
species
Variation Factors
Variation is influenced by two key factors
Environment – where and how we live
Inheritance – our genetic mix
Natural Selection
Charles Darwin
and Alfred Wallace
both provided that
mechanism
independently with
their theory of
Natural Selection.
A process by which the members of a species who are best suited
to their Environment are most likely to survive and reproduce
Introduction Evolution – includes all of the changes in the
characteristics and diversity of life that occur
throughout time.
Evolution can occur on both large and small
scales either Microevolution and
Macroevolution
The concept of evolution, that organisms may
change over time, was not new in Darwin’s
time. However, it was not a widely accepted
concept because no one understood how it
could work.
A mechanism was missing.
Natural Selection
In any population of organisms there is natural variation.
Some of these variations will allow the organisms possessing them to survive and reproduce better than those without these particular traits.
Natural Selection - Example
Resources that organisms need to survive are limited. Food, water, shelter, nesting sites, etc.
If there are not enough resources for all of the individuals, there will be competition for those resources.
Survivors represent a small part of the individuals produced each generation.
The successful traits will spread through the population.
This change in the frequency of alleles in the
population is evolution.
Natural Selection Environmental Change – Peppered Moth
Adaptation
A species may become adapted to its
environment in response to environmental
pressures.
A trait may be favored due to enhanced
survival or reproduction when faced with a
particular aspect of the environment.
Evidence of Evolution Comparative Anatomy
Anatomical similarities between organisms support the idea
that these organisms evolved from a common ancestor.
Natural Selection –Environment change – The Horse
Natural Selection – Primate Evolution
Human Interaction and
Evolution of Species
Other Methods of Genetic Change
Natural selection is not the only way that
allele frequencies can change from one
generation to the next.
Genetic Drift – a random loss of alleles.
Mutation – a new mutation can add alleles.
Nonrandom mating – inbreeding increases
the number of homozygous traits.
Natural Selection – Important
Points
Natural selection is not random. It occurs
in response to environmental pressures
and results in adaptation..
Charles Darwin and Alfred Wallace
developed theories on Natural Selection.
Natural Selection explains Evolution.
Evolution is the gradual change in the
inherited characteristics of a species over
time.
Evolution can lead to new species